Concrete Sections Research Articles

Experiments and FE Modeling on the Seismic Behavior of Partially Precast Steel-Reinforced Concrete Squat Walls

This paper proposed an innovative precast steel-reinforced concrete (PPSRC) squat wall to simplify on-site construction. In PPSRC squat shear walls, the hollowly precast RC wall panel can be assembled on-site through the pre-erected steel shapes, and the boundary cores will be filled using fresh concrete together with the slab system. The seismic performance of PPSRC squat walls, influenced by different construction techniques (cast-in-place vs. precast) and steel ratios, was examined through pseudo-static experiments on three specimens. Some key performance indicators, including hysteretic behavior, skeleton curves, stiffness degradation, energy dissipation, and load-carrying capacity, were analyzed in detail. The test results indicated that all the PPSRC squat walls failed in typical shear failure, and no significant slippage between the precast and fresh concrete sections was observed during the loading process, indicating that the composite action could be fully achieved via the novel throat connectors. In addition, the PPSRC squat walls could achieve comparable seismic performance compared with that of cast-in-place SRC shear walls (the peak load of the PPSRC squat wall only increased by 0.26% compared with the control specimen), and the load-carrying capacity and deformability could be enhanced by increasing the steel ratio in the boundary elements. Finally, an elaborate finite element model was developed and validated using ABAQUS software. The parametric analysis of the concrete strengths of precast and cast-in-place parts and the axial load was conducted further to investigate the seismic performance of PPSRC squat walls.

Experimental study of deconstructable embedded bolted shear connectors in composite beam subjected to cyclic loading

Bolted shear connectors have recently been introduced and studied as a convenient and demountable alternative for shear studs in steel-concrete composite beams. The major problem of welded studs is their undeconstructability. Bolted shear connectors make it possible to deconstruct and reuse the connection after its service life. In this study, the cyclic behavior of embedded bolted shear connectors in steel-concrete composite beams was investigated. The specimens included prefabricated concrete slabs with a square hole, which was filled with grout after assembling the concrete slab and steel section. Eight specimens were fabricated and tested to examine the effect of the bolt's diameter and strength on the cyclic behavior. To determine its behavior characteristics force-slip curves were applied. Ductility, strength degradation, and energy dissipation were the primary parameters investigated in this study. The results showed that the bolt’s diameter and strength significantly influenced the cyclic behavior of composite beams. Increasing the bolt's diameter and strength improved the connection's ductility and energy dissipation. Furthermore, doubling the bolt's cross-section increased the connection's ultimate strength by more than twice.

Proposing New Standard and ANFIS Calculation Approaches for Precast Concrete Connections with Steel Tube Elements: Lessons from Experimental Studies

The importance of establishing a proper method for calculating newly studied structural elements and primarily translating the results of experimental and numerical analyses into practical standards poses a significant challenge for structural researchers. In this study, which focuses on the importance of previously studied connections for the precast industry as a case study, two approaches are proposed for calculating the capacity of elements connected by rectangular steel tubes. The first approach involves a step-by-step calculation for analyzing the forces and capacities of different steel tube or concrete section parts under bending and shear, aiming to establish a standard calculation approach. Despite its complexity, the standard calculation approach has proven its accuracy by successfully solving examples with features similar to those of the experimental tests describing the process. The second approach relies on a look-up table generated from experimental data, developing an Adaptive Neuro-Fuzzy Inference System (ANFIS) for interpreting the data. ANFIS not only facilitates the evaluation of the capacity of non-experimentally tested elements but also resembles the calculation process. Evaluating ANFIS’s performance concerning the original results underscores its remarkable capacity to analyze experimental data. With a maximum calculation error of only 13% when compared to the experimental tests, ANFIS demonstrates considerable accuracy and user-friendliness. Following the initial internal force evaluations, the proposed standard calculation method requires eight specific control inputs, and comparing these inputs with experimental tests further confirms the effectiveness and safety of this approach for connection design.

Punching shear behavior for flat slabs with CFRP and openings

This study is devoted to investigate the flexural behavior of geopolymer flat slab that have transverse web openings with CFRP. The shear reinforcement is considered one of the important solutions to increase the resistance of the slabs to the failure of the punching shear and it is also possible through the use of these collars to provide service openings next to the columns. Three molds made of wood were prepared to examine 15 samples of geopolymer concrete under concentrated conditions, Dimensions of section are of total (70*70*7 cm) and Dimensions of column (15*15*15 cm). Three groups of models comprise the models for this research: the first group looks at the impact of the column's location; the second group looks at the impact of an opening next to the column or not; and the third group looks at the impact of CFRP. The findings demonstrated that the presence of transverse web openings affects the general flexural behavior of flat slab geopolymer reinforced concrete as a result of the reduction of concrete within the geopolymer concrete section. CFRP specimens demonstrated superior due to the inherent mechanical properties of the material. Among the various repairing procedures used, the full wrapping technique yielded the best results after the repairs.

Evaluation of glass fiber-reinforced polymer bars for application in sections of reinforced concrete

In order to evaluate the effectiveness and acceptability of glass fiber reinforced polymer (GFRP) bars as a substitute for conventional steel reinforcement, this study looks into their use in reinforced concrete sections. To assess the mechanical qualities of GFRP bars, the research includes mix design, casting, and extensive testing, such as flexural and tensile tests. Furthermore, a comprehensive study of GFRP-integrated reinforced concrete building sections is carried out, looking at factors like primary stresses, bending stresses, shear stresses, and deflection. Additionally, using ANSYS software, a comparative study of beam-column junctions using GFRP and RCC sections is conducted to evaluate structural performance under various loading circumstances. The results demonstrate how GFRP bars can improve building projects' structural integrity, toughness, and sustainability

The One-Dimensional Flow Pressure Loss Correction Model Based on the Particle Flow through Concrete Bend

The rheological behavior of concrete pumping in the bend section is complex. The existing conversion calculation for pumping pressure loss based on the straight pipe section often fails to meet engineering precision requirements. This paper develops a pressure loss correction model for a concrete pumping bend section based on a new one-dimensional flow model for the straight pipe section simulation of particle flow; the study analyzes the impact of parameters such as elbow shape and pumping flow rate on pressure loss. An equivalent conversion relationship between the bend section and the straight section is established. The comparison with the measured pressure values from the project shows that the relative error between the pressure loss values calculated by the correction model and the actual measurements is 15.8%.

Determination of Thermal Properties of Autoclaved Aerated Concrete Wall Sections Constructed with Distinct Mortars by the Experimental and Theoretical Data

This study investigated the thermal properties of autoclaved aerated concrete(AAC) wall sections constructed with distinct mortars. Within the scope of the study, four distinct wall sections of 25x25x5cm dimensions were created using AAC special adhesive mortar, cement mortar, lime mortar and cement-lime mortar. The thermal conductivity(λEXP) that was determined by the heat flow meter(HFM) method and bulk density(ρEXP) of each wall section was determined in the laboratory. Specific heat values(cEXP) of mortars and aerated concrete material were determined experimentally in the study. The thermal diffusivity value(αEXP), thermal effusivity value(eEXP) and volumetric heat capacity(VHCEXP) of each wall sample were calculated using the experimental data obtained in the laboratory. In addition, αTEO, eTEO and VHCTEO of each wall sample were calculated theoretically using the thermal conductivity, bulk density and specific heat value given in the literature and standards for the same wall sections. In the study, experimental data was compared to the theoretical data. As a result, the thermal properties of walls constructed with distinct mortars and thermal differences formed in the walls due to the effect of these mortars could be determined with experimental data. However, it was observed that theoretical data were insufficient to detect these thermal differences.

Evaluation of retrofitting effect of concrete filling in hollow RC columns using XFEM

Hollow RC columns are widely utilized in the construction of high piers in mountainous regions. Recently, precast hollow RC columns have been increasingly used to enhance transportability and ease of handling, aiding Accelerated Bridge Construction. This paper evaluated the effectiveness of concrete-filling retrofitting measures for hollow RC columns using eXtended Finite Element Method (X-FEM). Our focus was particularly on instances where original hollow sections and post-filled concrete sections don't behave as unified structures. The proposed X-FEM model's reliability was validated through simulations replicating compressive strength tests on molded concrete specimens and previous static loading tests on hollow RC columns conducted to evaluate the efficacy of concrete-filling retrofitting for hollow RC columns. The proposed X-FEM model successfully represents the compressive softening and fracture behavior of concrete under uniaxial compression. It also successfully replicated the lateral load capacity and the crack patterns of hollow RC columns observed in the previous experiments. When comparing the component ratios of bending and shear deformation of the columns, the shear deformation component of the hollow RC column retrofitted with the concrete filling was about 1.5 times larger than that of the solid RC column at each displacement. This result indicates that concrete-filling retrofitting might not enhance the shear capacity of hollow RC columns to the anticipated level in scenarios where the pre-existing hollow portion and the post-filled concrete portion fail to function as unified structures. Based on these findings, this study investigated the efficacy of anchor reinforcement in hollow RC columns filled with concrete to enhance the structural unity of existing and filled portions. The results indicate that anchor reinforcement improved the shear resistance properties by enhancing the structural unity between the pre-existing hollow portion and the post-filled concrete portion.

Seismic Vulnerability Assessment of Non-Overflow Concrete Gravity Dam Section

Abstract As the economy advances, there is a growing need for energy. Harnessing hydroelectric energy has emerged as a crucial strategy for addressing the energy crisis. To promote hydropower development, numerous tall concrete dams are either under construction or in the planning stages. These dams are frequently situated in areas with elevated water levels and face the challenge of being located in regions with high seismic intensity. An accident resulting from the failure of concrete dams can pose significant threats to both economic development and public safety. Therefore, it is of crucial importance to investigate the stability of such dams, particularly under conditions of high water levels and seismic activity. The finite element program Geostudio is being undertaken to evaluate a complete numerical analysis of the dam. In this paper, Longtan Dam has been selected as the case study for the research. This study is applied in two cases: seismic and static conditions. A two-dimensional seismic numerical analysis was carried out using the Koyna earthquake acceleration time records in 1976. The results of the FEM model concluded that the dam is unsafe under sesmic conditions. The concrete-rock interface, particularly susceptible to sliding, was identified as the most critical part of the dam, presenting the most likely failure mode. The study highlights the significance of its methodology in investigating earthquake effects on dams, prioritizing it over the achieved results. The aim is for the conclusions and recommendations to provide valuable guidance for future studies and initiatives focused on enhancing safety at hydropower dams.

Experimental Study on Shear Strengthening of Reinforced Concrete Beams by Fabric-Reinforced Cementitious Matrix.

In this study, an experiment was conducted to investigate the shear performance of reinforced concrete (RC) beams strengthened using fabric-reinforced cementitious matrices (FRCM). Four reinforced concrete beams, including a control specimen, were fabricated, and the shear strengthening effect of the FRCM was investigated on eight shear specimens, with the strengthening type and shear reinforcement as key variables. In particular, the digital image correlation (DIC) technique was applied to closely analyze the deformation of reinforced concrete beams subjected to shear forces. The average shear strain-shear stress curve of each specimen was derived, and the contributions of shear and bending to the vertical deflection and the change in the principal strain angle with increasing shear force were analyzed. The experiment results showed that all specimens failed with diagonal cracks within the shear span. In the specimens without shear reinforcement, the shear strength increased by up to 65% according to the FRCM strengthening, while in the specimens with shear reinforcement, only the sided bond strengthened specimen showed a strength increase of 16% compared to the control specimen. Based on displacement data of the DIC, it was confirmed that FRCM strengthening can control the deformation of the RC beam. To evaluate the shear strength of the FRCM-strengthened RC beams, a shear strength model was proposed by considering the contributions of the concrete section, shear reinforcement, and FRCM. The proposed model was capable of reasonably evaluating the shear strength of RC beams strengthened with FRCM, considering the shear contribution of FRCM and bond capacity between FRCM and concrete substrate, in which the shear strength of specimens was underestimated by 28% to 35%.

Finite Element Analysis of CFFT and CFDTS Columns as a Replacement for CFST Columns in Composite Construction by Using ABAQUS

In the field of composite construction of steel and concrete, concrete filled steel tube CFST columns have been proven to be greater performance structural members. The properties of steel and concrete are used efficiently. But CSFT columns are prone to corrosion in outdoor structures as the outer encasing tube is made up of steel. The outdoor use of CFST column due to its high risk of corrosion requires frequent maintenance and may prove costly. Hence, the possible replacement of steel tubes with fiber-reinforced polymer (FRP) Tubes has to be investigated. FRPs are the most suitable material for encasing concrete columns due to its orthotropic behaviour. In solution to this, the paper is aimed at numerical study of CFST, CFFT and CFDTS short columns to study the axial compression behavior of these short columns analytically and examine the best suitable alternatives of CFST column. The concrete in-fill double tube section CFDTS with better axial compression, stiffness and ductility are also investigated as a suitable replacement of CFST columns. For these three different specimens of CFST columns of steel tube thickness 3mm, 4.5mm and 6mm, CFFT columns of GFRP tube thickness 3mm, 4.5mm and 6mm and CFDTS column with GFRP outer tube of thickness 3mm, 4.5mm and 6mm as well as inner steel tube of thickness 1.5mm, 2mm and 2.5mm are analyzed and compared. Consequently, CFDTS columns, with 1872 kN are proven to be superior to CFST columns with axial capacity 1653 kN and CFFT with axial capacity 689 kN columns. The confinement effect in CFDTS is more than CFST and CFFT column.

Non-linear response of confined concrete beam-column structures under horizontal loading

In this study, a behavior law for confined concrete is considered with the introduction of transverse reinforcement to increase the compressive strength of concrete, using the model of Mander et al. This model integrates the confinement effects provided by transverse reinforcement, enhancing the load-bearing capacity of concrete under compressive stress. A pushover analysis is carried out on a full-scale, four- levels structure, using the N2 method. This advanced technique combines non-linear static analysis with inelastic response spectra. Using this approach, the structure's seismic performance can be estimated, accounting for its ductility and the non-linear effects at each loading stage. The inelastic response spectra are adjusted using reduction factors based on the structure's capacity to dissipate seismic energy through inelastic deformations. By varying the confinement rate of the concrete sections, different performance points of the structure can be obtained. The confinement ratio is a crucial parameter influencing the ductility and strength of confined concrete. Closer spacing of transverse reinforcement increases the confinement ratio, which improves the concrete's deformation capacity and ultimate strength. The results show the effect of the behavior law used to consider concrete confinement on the performance points of the structure. In particular, it is observed that increasing the confinement leads to significant gains in the strength and ductility of the structure. These results highlight the importance of optimally using transverse reinforcement to design structures that ensure their performance and safety under seismic loads.

Structural performance of fibre reinforced recycled aggregate concrete road kerb sections under monotonic and cyclic loading

In recent years, there has been a notable emphasis on waste reduction and the adoption of recycled materials within the construction industry to reduce the industry’s overall carbon footprint. This study investigates the structural performances of concrete kerb sections prepared with five different concrete mixes containing recycled concrete aggregate, recycled tyre-derived aggregates and recycled polypropylene fibres. Kerb sections were cast at a road site in a suburb of Adelaide, Australia. After the concrete hardened, sections were cut and brought to the laboratory. A large number of monotonic and cyclic load tests were conducted on the kerb sections. The load-carrying capacity, bending moment capacity, cyclic fatigue capacity, durability properties along with deformation tolerance were evaluated. Kerb sections made with concrete containing recycled aggregate and polypropylene fibre could sustain nearly 2000 cycles of loading. Kerb sections prepared with natural aggregate concrete performed comparatively better. The addition of polypropylene fibre significantly improved the post-cracking behaviour of kerb sections and can delay crack propagation and other distress when subjected to cyclic loadings such as excessive soil movement, e.g., in areas with expansive soils or prone to tree root migration. Long-term observation may be required to confirm the mechanical and durability performance improvement in real field conditions.

Structural design of reinforced concrete frames for minimum amount of concrete or embodied carbon

In standard engineering practice, designers often aim to minimize the amount and volume of concrete in reinforced concrete (RC) frames by reducing the size of member cross-sections. This is done either for architectural reasons or because it is assumed to drive to more economic and environmentally friendly productions. The present study, for first time, compares the environmental footprint of RC frames designed for minimum concrete volume against designs for minimum embodied carbon. To serve this goal, six realistic 3D RC building frames are optimally designed for parametric values of the carbon factors of concrete and reinforcing steel materials. In this comparison, it is noticed that the carbon factors ratio R of reinforcing steel to concrete plays a key role. More particularly, it is found that for R ≤ 10 the designs for minimum concrete and carbon practically coincide. This is a useful observation since it signals a clear direction to designers to decrease concrete sections to achieve minimum environmental impact. Nevertheless, as R increases from 10, the two designs gradually deviate since the carbon footprint of rebars becomes more important. For high R values, the RC frames with the least amount of concrete produce, on average, up to 40 % more embodied carbon than the most environmentally clean designs.

Colour pervious concrete pavements applied to bikeway track: mechanical, hydraulic and functional performances

ABSTRACT Pervious concrete pavement test sections employing coloured permeable concrete were constructed as an experimental bicycle lane. For two of the sections, coloured concrete was used with pigment addition consisting of Fe2O3 (red) and Cr2O2 (green). The impacts on the resistance and stiffness of the concretes when using these pigments were analysed in relation to the reference concrete (grey). Alterations in plasticiser dosage during mixing were readily observed with the red concrete. The flexural strength increased substantially in the case of the red coloured concrete, as well as the modulus of elasticity of the material. Initial infiltration rates decreased with the use of coloured pigments, especially for red concrete, with expressive drops in permeability. Simultaneously, the resistance to friction given by the British Pendulum Number was reduced due to the use of red or green pigments. The consequences of using red pigment with a very high grains specific surface are discussed, since they are advantageous in the case of mechanical responses eventually inferior in terms of hydraulic and functional aspects.

Design cost minimization of a reinforced concrete column section using overnew swarm-based optimization algorithms

It is very tiresome for a practiser to detect the best feasible sizing design of structural members including reinforced concrete columns that is a highly nonlinear and complicated structural engineering optimization problem. This is due to such a design is practically conducted via conventional trial-and-error computing methods in which resistance to external loads, cost efficiency, and aesthetic factors, etc. have to be considered. This study focuses on minimizing the design cost of primarily proposed reinforced concrete column design problem via three overnew swarm-based optimizers such as Coati Optimization Algorithm, Fox Optimizer and Pelican Optimization Algorithm (POA) that are firstly utilized for this purpose. In this regard, the type of steel rebar distribution, the characteristic strength of the concrete, the height and width of the column section, and the number and diameter of the rebars are treated as discrete design variables of the newly proposed complex reinforced concrete column design cost optimization problem. In solution, the design requirements specified in practice code provisions should also be met. Here, Turkish Building Earthquake Code 2018 specifications are considered as practice structural design constraints. Consequently, the algorithmic performances of three overnew swarm-based metaheuristic optimization algorithms are compared and evaluated in detail. Amongst them, the POA shows most fruitful algorithmic design solution performance.

Feasibility of Repairing Concrete with Ultra-High Molecular Weight Polyethylene Fiber Cloth: A Comprehensive Literature Review

This review explores the use of Ultra-High Molecular Weight Polyethylene (UHMWPE) fiber cloth as an innovative solution for the repair and reinforcement of concrete structures. UHMWPE is a polymer formed from a very large number of repeated ethylene (C2H4) units with higher molecular weight and long-chain crystallization than normal high-density polyethylene. With its superior tensile strength, elongation, and energy absorption capabilities, UHMWPE emerges as a promising alternative to traditional reinforcement materials like glass and carbon fibers. The paper reviews existing literature on fiber-reinforced polymer (FRP) applications in concrete repair in general, highlighting the unique benefits and potential of UHMWPE fiber cloth compared to other commonly used methods of strengthening concrete structures, such as enlarging concrete sections, near-surface embedded reinforcement, and externally bonded steel plate or other FRPs. Despite the scarcity of experimental data on UHMWPE for concrete repair, this review underscores its feasibility and calls for further research to fully harness its capabilities in civil engineering applications.

Design method and seismic vulnerability of bridges using UHPC-NSC composite pier

The focus of this investigation is the application of ultra-high-performance concrete (UHPC) and normal strength concrete (NSC) in constructing composite piers. The UHPC-NSC composite pier, comprising the external UHPC jacket and internal NSC, demonstrates a marked enhancement in both load-bearing capacity and control of seismic damage. However, the lack of suitable seismic design methodologies presents a significant barrier to the practical application of the composite pier. Drawing on extensive experimental and theoretical research, this paper proposes an optimization formula that determines the diameter of the composite pier and the thickness of the UHPC jacket. This formula aims to maximize the use of UHPC material, manage the damage, and equalize sectional moment resistance with the original reinforced concrete section. Utilizing the proposed design approach, UHPC-NSC composite piers were implemented in a typical continuous beam bridge. Seismic vulnerability analyses were conducted to quantitatively substantiate the performance of the composite pier following the aforementioned design approach. The analysis affirmed that the composite pier effectively reduced the exceeding probability of all damage levels under small and moderate earthquakes, and extensive damage level under strong earthquakes.

Performance study of low temperature air heated rock bed thermal energy storage system

AbstractOne of the primary types of sensible heat storage systems in drying applications is the packed rock bed. However, to create large‐scale heat storage systems for industrial use, one must comprehend the hydrodynamic and effectiveness of the heat transport mechanism inside the bed. In this study, the thermal storage unit uses river rock as heat storage materials with equivalent particle diameters of 36 mm in bed 1 and 56 mm in bed 2. The rocks were stacked in a truncated cone‐shaped concrete wall section with an average diameter and depth of 1.1 m and 1.3 m, respectively and a volume of 2.32 m3. During the charging phase, two airflow configurations were used, one from the top with an air mass flow rate of 0.753 and 0.332 kg/m2‐s and the other from the bottom with an air mass flow rate of 0.955 kg/m2‐s. During the discharging phase, the entire flow configuration is from the bottom section. It was observed that the mass flow rate and particle equivalent diameter had an important effect on the thermal performance and behaviour of the rock bed during charging and discharging operations. Maximum efficiency was achieved with an airflow configuration provided from the bottom when charging at 0.955 kg/m2.s. Consequently, a sizable quantity of heat or energy (60 MJ) was retained. It was also observed that the relationship between air mass flow rate and particle size was significant, with smaller particles retaining more energy. When comparing bed 1 with bed 2 at this air mass flow rate, bed 1 stored 2.1 times more energy than bed 2. A wind tunnel experiment was used to measure the pressure drop in the packed rock bed. The pressure drop in the bed increases with an increase in particle Reynolds number and decreases with an increase in particle size. Rock bed heat transfer coefficient and Nusselt number were calculated using the correlation that has already been established in the literature smaller particles showed higher heat transfer coefficients and lower Nusselt numbers. This is due to the increase in particle‐to‐particle interaction and larger particle surface areas. For a given Reynolds number, the Nusselt number increases with the size of the rock particle.

STRENGTH DESIGN OF REINFORCED CONCRETE SECTIONS BASED ON A NUMERICAL OPTIMIZATION METHOD

Reinforced concrete structures are widely used in construction of civil infrastructures. Classical methods are available for the analysis and design of reinforced concrete members, such as beams or columns, which are typically done by hand or using a spreadsheet program. In this study, an analysis and design approach of reinforced concrete sections is developed based on a numerical optimization method, and applied in accordance with the latest concrete design code. The basic idea of the proposed approach is to derive an optimization formulation in order to determine the minimum steel area required to support a given factored load combinations applied on a concrete section. A rigorously derived analysis and design framework of general beam sections is presented. For practical applications by civil and structural engineers, the readily-available optimization solver in Microsoft Excel spreadsheet is used. To illustrate the applicability of the approach, a numerical example with different analysis and design cases is studied. The proposed analysis and design approach using numerical optimization and spreadsheet solver works very well and is easy to implement in the Excel environment. The analysis and design results compare well with hand calculation results based on the classical method.